Method of coating cathode-ray tubes



April 2, 1968 J. P. FIORE METHOD OF COATING CATHODE*RAY TUBES 2Sheets-Sheet 1 Filed 001;. 20, 1964 Aprifl 2, 1968 J. P. FIORE METHOD OFCOATING CATHODE-RAY TUBES Sheet 2 M ENTOR 1/ 056793 231* LOTQ I BY 2Sheets Tilt Angle Filed Oct.

Time

3,376,153 METHOD 6F ATING CATHGDE-RAY TUBES Joseph P. Flore, Wheeling,lll., assignor to The Rauiand Corporation, Chicago, 111., a corporationof Illinois Filed Oct. 20, 1964, Ser. No. 405,076 Claims. (Cl. 1l733.5)

ABSTRACT OF THE DISCLOSURE In the disclosed method of coating acathode-ray tube, the cap section of the tube is supported in ahorizontal plane with its flange extending upwardly and coating materialis deposited on the central surface of the cap in an amount exceedingthat required to coat the screen area. The cap is then tilted andconcurrently rotated at speeds selected in relation to the charge andviscosity of the coating material to distribute the material uniformlyover the screen as the cap is tilted to an angle of about degrees fromthe horizontal. Tilting is then interrupted and the excess coatingmaterial is removed while the rotation of the cap is continued.Thereafter, the tilting is resumed and the cap is quickly displaced toan angle of the order of 90 degrees relative to the horizontal and,while in that position, the coating is dried by rotating the cap at ahigher speed in front of suitable heaters.

The present invention concerns a method of coating a cathode-ray tubeand is useful in the fabrication of monochrome tubes but is even moreapplicable to the screen forming procedure of tri-color cathode-raytubes. For convenience, it will be described in connection with thelatter type of device.

The color cathode-ray tube currently in commercial use is of theso-called shadow-mask variety. It has a screen which bears a regularinterlaced pattern of phosphors which, when energized by electrons, emitlight of the primary colors. Usually all three primaries are employedand the screen has a repeating pattern of phosphor triads, that is, ofclusters of three phosphor dots each of which is capable of emittinglight of one of the three primary colors.

While such a tube may utilize a single electron gun, it is customary toemploy a family of three guns disposed in a delta arrangement. Each gundevelops an electron beam which is directed toward the screen and eachbeam is permitted to impact upon phosphor dots of a single assignedcolor. This color selection or assignment of a particular gun to aparticular color phosphor is accomplished by means of a shadow-maskwhich is a mask having a pattern of apertures corresponding to thepattern of triads on the screen, usually with one aperture in the maskfor each triad on the screen. The fabrication of such a device is adifficult process especially in the formation of the screen.

A variety of ways have been suggested for depositing phosphor dots onthe internal surface of the tube faceplate which serves as the screenarea. It is known, for example, to apply the phosphors throughtechniques of dusting, printing, electrostatic deposition and so forth.The present invention concerns what has become to be known as the slurryprocess of screen formation. It should be observed in passing that themethod to be described is also of use in filming the mu1ti-colorphosphor screen preparatory to aluminizing.

In the slurry process, a slurry mix is prepared of a photosensitiveresist and the particular phosphor that is to be applied. A measuredquantity of this slurry is deposited in the center of the screen portionof the cathode-ray tube which, at this juncture in the manufacturingprocess, is merely the faceplate of the tube bounded by a peripheralflange and is supported in plane canted to the vertical. The quantity ofslurry deposited is much in excess of that re- 3,376,153 Patented Apr.2, 1968 quired to form a uniform layer over the screen of the tube and auniform distribution of the slurry is achieved by rotating the tiltedscreen or cap, as it is referred to, at a high speed. Much of the excessslurry accumulates at the meeting area of the screen and the flange dueto the influence of centrifugal force and a probe may be inserted intothat area as the cap rotates in order to draw off most of the excessslurry. After removing such excess, the slurry coating is dried and thetube cap is equipped with its mask and positioned on an exposure devicewhere selected areas are exposed to a radiation, such as ultravioletlight, which causes the exposed areas of the coating to become insolublein water. Exposure through the mask in this fashion subjects separateddots or small islands of the coating to the radiation so thatdevelopment of the coating thereafter establishes a field or pattern ofdots of the particular phosphor that has been contained in the slurry.Repeating this general process three times and with appropriategeometrical positioning of the exposure source permits the formation ofthe phosphor triads on the cap or screen of the tube.

The described process has proved satisfactory in the manufacture ofround tubes but its application to tubes of other configuration,specifically to rectangular tubes, is obviously diflicult. For example,the slurry tends to develop swirls at the corners of the cap which maycause irregularities or non uniformity in the coating and, additionally,the use of a simple probe to remove excess slurry is no longer feasiblebecause of the abrupt changes in contour of the flange surrounding thescreen area.

Accordingly, it is a specific object of the invention to provide a novelmethod of coating the internal surface of the screen portion of acathode-ray tube.

A further object of the invention is to provide an improved method forcoating the screen area of a color cathode-ray tube by the use of aslurry.

A specific object of the invention is to provide a new and improvedmethod of slurry coating a tri-color cathoderay tube that is usefulirrespective of the specific configuration of the tube beingmanufactured.

Still another specific object of the invention is to improve the slurrycoating method of screening a color cathode-ray tube to minimize thedeposit of slurry on the flange that borders the periphery of the screenarea.

The method of the invention for selectively coating the internal surfaceof the screen portion of a cathode-ray tube comprises supporting the capin a horizontal plane with its peripheral flange extending upwardly anddepositing upon its screen surface a quantity of viscid coating materialin an amount substantialy exceeding that required to coat the screen.The cap is then rotated at a first speed and concurrently tilted todistribute the coating material over the screen. Thereafter the tiltrate is increased to quickly position the cap in a predetermined tiltplane, preferably about 100 degrees, and the cap is rotated in thatplane at a speed which is higher than the first rotational speed to drythe coating on the screen.

The features of the present invention which are believed to be novel areset forth with particularity in the appended claims. The invention,together with further objects and advantages thereof, may best beunderstood by reference to the following description taken in connectionwith the accompanying drawings, in the several figures of which likereference numerals identify like elements, and in which:

FIGURE 1 is an elevational view, partially broken away, of a screeningapparatus for practicing the coating method of the invention;

FIGURE 2 is a view taken along line 22 of FIG- URE 1;

FIGURE 3 is a side elevational view taken as indicated by line 33 ofFIGURE 2;

FIGURES 4-6, inclusive, are functional views used in describing themethod carried out by the apparatus of FIGURE 1; and

FIGURE 7 comprises curves used in explaining the coating method of theinvention.

Before describing the apparatus represented in the drawings and thecoating process that it performs, it is appropriate to consider thestructure of the tube being processed, at least that part of thestructure that is to be operated upon by the coating apparatus. Where aslurry coating technique is to be employed, especially if the tube is tohave a tri-color phosphor screen, the envelope comes in two initiallyseparate parts. One part is the cap which includes the faceplate of thetube bounded by a peripheral flange and the internal surface of thefaceplate serves as the screen portion. Of course, the process to bedescribed may also be employed in the fabrication of a screen packwherein the screen structure is separate from the tube envelope butcurrent practice is to have the internal surface of the cap constitutethe image area. The other envelope portion is the conical section whichterminates at its smallest diameter in the cylindrical neck which is tohouse the gun assembly. After the screen has been formed and after theaperture mask has been installed, if the tube is of the shadow-maskvariety, the cap and funnel portions are united by a frit seal and theenvelope is then ready to receive the gun assembly, the base and soforth. The cap may either be round or rectangular and, of course, themeeting surfaces of the cap and funnel sections have identicalcross-sectional configurations and dimensions.

The apparatus of FIGURE 1 for coating the cap section of a cathode-raytube has a frame structure 10 supporting a driving motor 11 which drivesa link chain 12 through a variable speed reducing gear system 13. Thedriving speed of the chain is selectable by means of a speed selectionlever 14 that may be displaced between either of two positions by meansof a hydraulic cylinder 15 the piston of which mechanically couples tolever 14.

Link chain 12 extends the driving system to a shaft 16 which carries agear 17 near one end for engaging link chain 12 and a bevel gear 18 atits opposite end. Shaft 16 is supported by means of a bearing block 19and also by a housing 20 in which gear 18 is enclosed. Finally themechanical drive is continued through another bevel gear 21 inengagement with gear 18 and affixed to a shaft 22 extending throughhousing 20 and carrying at its forward end a workholder 23 for removablysupporting the cap 5 of a cathode-ray tube being processed. Theworkholder is a spider type of structure with three arms extendingradially from a hub and having a lock 23a (FIG- URE 3) which may beclosed to lock the tube cap within the holder. It is desirable tointerpose resilient pads on the inner faces of the arms of workholder 23to avoid damage to cap 5. The mechanism as thus far described permitscap 5 to be mounted in position within the coating apparatus and to berotated at any one of two selected speeds.

In addition to being rotated, workholder 23 and the cap which itsupports are subject to la tilting movement in order to control theangle of the cap with respect to a reference plane such as thehorizontal bed or plane of the coating apparatus. For this purpose thereis a second shaft 30 in coaxial alignment with shaft 16, supported by abearing block 31 and also extending into housing 20. A flange coupling32 secures housing 20 to shaft 30 so that they rotate together about theaxis of shafts 16, 30 although shaft 16 rotates independently of housing20. The drive for shaft 30 comprises a second link chain 35 whichthreads over a gear 36 at one end of shaft 30 and an idler gear 37rotatably supported on a shaft 38' at the base of frame 10. Displacementof chain 35 and rotation of gear 36 is under the control of anotherhydraulic cylinder 40 which has a piston rod mechanically coupled bymeans of a link 41 to chain 35. By virtue of this mechanical coupling,rectilinear motion of the piston of cylinder 40 occasions displacementof shaft 30 and tilting of workholder 23.

The coating process involves programmed changes in both the angle oftilt and the speed of rotation of the workholder. These parameters arecontrolled, in part, by a family of cams that are carried by a shaft 45rotatably supported in bearing blocks 46. Shaft 45, is drivenconcurrently with tilt shaft 30 by means of another link chain 47engaging a gear 48 carried by tilt shaft 30 and a gear 49 carried by camshaft 45. The family ofcams on shaft 45 are two limit cams 45a and 45dand two other cams 45b and 45c which control programming of the tiltingand rotating of workholder 23. Their control is exercised through acontrol system 50 of conventional design which includes timers as wellas electrically actuated valves for admitting fluid under pressure tocylinders 15 and 40 and to another cylinder 55 (FIGURE 1) which controlsthe position of a panel 56 slidably supported on the front portion offrame 10 of the coating apparatus. The coupling of panel 56 to thepiston rod ofcylinder 55 is by means of a cable 57 passing over suitablerollers supported on the frame of the coating machine. Conduits 63extend from the various hydraulic cylinders to control system 50 forconveying a fluid under pressure required to displace the piston of anyof these cylinders in a particular direction determined by the admissionof fluid into one end or the other of its associated cylinder in theusual way.

Panel 56 carries a housing 58 in which are mounted a series of infraredheaters 59. The housing of the heaters may be polished to be reflectingand the side thereof which faces workholder 23 is open in order thatheat may be directed from housing 58 into the tube cap being processed.

Also secured to the frame of the machine is a large enclosure 60 havingan aperture 61 to be closed by housing 58 when panel 56 is in its lowerposition. Enclosure 60 protects workholder 23 from the atmosphere duringmuch of the coating process so that foreign particles are not admittedto the cap being coated. There is a further container or shield 62secured to the mount of workholder 23 and enclosing the workholderexcept for its forward portion. This is to confine the coating materialand protect against scattering.

The coating method of the invention may be carried out by the describedapparatus and is best explained by considering an illustrative cycle ofthe machine. Initially or at the start of any cycle, the apparatus isconditioned as represented in FIGURE 1 with panel 56 in its extremeupper position to have workholder 23 available or accessible throughopening 61 ofenclosure 60. The cap 5 of a cathode-ray tube which is tobe processed is inserted into workholder 23 and locked in position. Itwill be apparent in FIGURES 1 and 3 that the cap is supported in a planewhich is slightly in excess of the vertical,

approximately to degrees in relation to the bed operator which causescontrol system 50 to admit fluid under pressure to cylinder 55.and lowerpanel 56 to its lowermost position in which opening 61 of enclosure 60is closed by the panel and heater housing 58.-Concurrently controlsystem 50 actuates the hydraulic system to admit fluid under pressure tocylinder 40 at a reasonably fast rate to cause its piston to descendandrotate shaft 30 and along with it workholder .23 in a clockwisedirection as viewed in FIGURE 3. At this time, control system 50 isunresponsive to the. series of cams on shaft 45 and remains so untillimit cam 45a has operated its cam follower. This occurs when workholder23 has positioned cap 5 in a horizontal plane as shown in FIGURE 4. Theeffect of limit cam 45a in displacing its cam follower is to terminateclockwise displacement of shaft 30 and workholder 23 by interrupting thefluid supply to cylinder 40 and to condition control system 50 torespond to the other cams on shaft 45.

With the cap in its horizontal position a second start button (notshown) is manually operated to actuate control system 50 and a measuredquantity of viscid coating material 6 is deposited upon the internalsurface of screen 5a. The quantity placed in the cap substantiallyexceeds the amount that is required for a uniform coating of screen 5a.While a variety of coating materials may be employed, for theillustrative case it is a photosensitive resist such as polyvinylalcohol with a phosphor that emits light of red, green or blue color. Anautomated coating dispenser may be utilized but the simple coatingapparatus represented in the drawing contemplates that the coating is tobe deposited manually. In the laboratory, for example, a cup or othercontainer of coating material is poured into the cap. The broken-linerepresentation 5 in FIGURE 3 of the workholder assembly makes clear thatthe cap is accessible from the portion of the machine rearwardly of theback panel of enclosure 60. As the coating material is poured into thecap, the dispenser is preferably moved or oscillated so that the wholecharge is not dumped into a particular spot at the center of the cap.Moving the pouring stream about, in the central area of the cap, lendsto uniformity of the coating.

Control system 59 includes a first timer which is operated when thesecond start button is pressed. The first functions controlled by thistimer are the energizing of motor 11 and the opening of the valvefeeding fluid under pressure to cylinder 40 to rotate workholder'23 at aconstant speed of about 5 r.p.m. and concurrently effect tilting orcanting of the workholder in a counterclockwise direction, also at aconstant rate. By properly adjusting the speed of rotation of workholder23 and the rate of its tilt, selecting these parameters in relation tothe viscosity and the amount of coating material poured into cap 5, thecoating material may be distributed over screen 5a by the time the caphas attained the position of FIG- URE 5 at which it is approximately atan angle of 30 relative to the horizontal reference plane. As indicatedin that figure, coating material 6 will now have been distributed overthe whole screen 5a. For slurries of the type used in commercialproduction of cathode-ray tubes today, having a viscosity of the orderof 25 to 100 centipoise, an acceptable tilt rate is one degree persecond and the displacement time from the position of FIGURE 4 to thatof FIGURE 5 is of the order of seconds.

The rate at which the workholder is tilted has a very pronounced effecton the coating pattern accomplished with the apparatus. It will beapparent that the deposit of slurry is heaviest and is subject to thegreatest gravitational force at the very start of the coating cyclebecause as the workholder is rotated and tilted the pool of coatingmaterial tends to traverse a spiral path, continually losing some of itsmass due to its viscid nature. As a consequence, the mass andgravitational effect decrease with coating time. Consequently, if thespeed and rate of tilt are maintained uniform, as represented by curve Aof FIGURE 7, the entirety of the screen area may be coated but thecoating will not have a uniform thickness. There will tend to be aheavier coating in the central portion of the screen than at the edges.Ideally, assuming a constant rate of rotation, the rate of tilt shouldvary as indicated by curve B of FIGURE 7 in order to attain uniformityof the coating over the entire screen area. That is to say, the rate oftilt decreases throughout the coating interval. The phenomenon may, forconvenience of explanation, be likened to settling in which a given timeis required to settle a coating of a particular thickness from asettling solution of a certain height but a longer settling period isnecessary to attain the same depth of coating with a settling solutionof lesser height. An acceptable compromise is the condition of curve C,indicating a uniform tilting rate for a certain period of time plusfurther rotation of the workholder at a fixed tilt angle.

By way of example, the workholder may be tilted at the aforementionedrate of one degree per second until the spiraling pool of coatingmaterial just spans to the edge of the screen area. When this point isreached, the tilt angle is maintained fixed and continued rotation ofthe workholder permits the coating at the edge portion of the screen toachieve substantially the same thickness as that of the remainder orcentral part of the screen. It is this coating method that is easilyaccomplished with the described apparatus in which timer number 1 ofcontrol system 51 interrupts the fluid supply to cylinder 40 andcounterclockwise rotation of workholder 23 when it has arrived at the 30tilt angle of FIGURE 5. The timer maintains thi condition for a measuredhold interval in which the Workholder continues to rotate but at a fixedangle of tilt.

With the workholder supporting cap 5 in this tilted plane excess coatingmaterial from screen 5a tends to drain downwardly in the direction offlange 5b and after a hold time of approximately 4 seconds, the excesscoating material is removed. One convenient way of removing the excesscoating is through the agency of a syringe 749 that may be immersed inthe pool of coating material as indicated in FIGURE 5. The excesscoating material is reclaimed, that is to say, when it is removed fromthe tube cap under process it is returned to the reservoir or supplyfrom which the initial charge has been taken. This is obviously easilydone by discharging the contents of syringe 70 into the reservoir.

The first timer of control system 5% affords a sufiicient interval forremoval of the excess coating material and at the conclusion of thatinterval once again admits fluid under pressure to cylinder 40 tocontinue the tilting of workholder 23 and the drive of cam haft 45 atthe original slow rate. At this juncture, the timer will have completedits program and shut oif. Immediately thereafter the rotation of shaft45 causes cam 45b to displace its follower and cause control system 50to admit fluid into cylinder 49 at a faster rate. As a consequenceworkholder 23 tilts at a much more rapid rate and in a very shortinterval cam 45c actuates its follower to cause control system 50 toadmit fluid under pressure to cylinder 14, displacing speed controllever 14 to its alternate position 14b (FIG- URE 3). This position ofthe speed selector cause the workholder to be rotated at a speed whichis high compared to its previous rotational speeds, an illustrativevalue is r.p.m.

In about 6 seconds workholder 23 returns to its initial position havinga tilt angle of the order of degrees, between 90 and degrees asindicated in FIGURE 6, and at this time limit cam 45d actuates itsfollower to initiate a second timer included Within control system 50.The first function performed by this timer is interruption of the fluidsupply to cylinder 4-0 and termination of the counterclockwisedisplacement of workholder 23. Concurrently the timer closes theenergizing circuit for heaters 59, permitting cap 5 to be dried while itis rotated at its high speed. After a suitable interval determined bythe second timer, about 4 minutes, heaters 59 are turned off, motor 11is de-energized, and fluid is admitted to cylinder 55 only long enoughto elevate panel 56 to its starting position. In short, the apparatus isrestored to its initial condition and the cycle has been completed. Theoperator may now release the coated cap from workholder 23 and direct itfor the further processing steps such as its lighthouse exposure anddevelopment none of which are of concern to the subject invention.

The speeds of the processing cycle are rather slow and the method may beeasily practiced in a manually adjusted apparatus. That is to say, bothcontrol of the rotational speed of Workholder 23 and its degree of tiltmay be performed manually by the operator with little difiiculty.

7 If desired, tilt cam 45b may be contoured to exercise control of aneedle valve in the supply conduit to cylinder 40 to control the fluidadmitted thereto and the tilting of workholder 23 in accordance withcurve B of FIG- URE 7. However, the described process of a constant tiltrate followed by a hold period is acceptable in tube production.

It will also be appreciated that the starting quantity of coatingmaterial has a direct bearing on the time required to coat. Experiencehas proven that a 25 inch rectangular cap may be coated with 200 cc. ofcoating material in approximately one minute although this necessarilyinvolves quite an excess of coating material Which may spread to flange51), especially during the high-speed rotation, and require the usualtrim operation. Generally 40 to 50 cc. of material is suflrcient to coatthe screen. On the other hand, the starting amount of coating materialmay, if desired, be only 75 cc. which has the distinct advantage thatvery little spreads to the flange and the trim step may be drasticallyreduced if not entirely eliminated but at the cost of coating timebecause the cycle with this small amount of coating material increasesto about four minutes.

Coating by means of the described process has distinct advantages inthat the specific configuration of the cap under processing is of noparticular consequence. The swirling or disturbances encountered at thecorners of a rectangularly shaped cup with other coating processes arecompletely avoided. Further, it may be arranged that only a minorfractional portion of flange b becomes coated at all so that trimming iseither obviated or greatly reduced with a commensurate reduction in thedanger of screen spoilage because of errors committed during trimming.

While particular embodiments of the invention have been shown anddescribed, it will be obvious to those skilled in the art that changesand modifications may be made without departing from the invention inits broader aspects, and, therefore, the aim in the appended claims isto cover all such changes and modifications as fall within the truespirit and scope of the invention.

I claim: 1. In the manufacture of a cathode-ray tube of the type havinga cap section with a screen portion bounded by a peripheral flange, themethod of selectively coating the internal surface of said screenportion which comprises:

supporting said cap in a horizontal plane with said flange extendingupwardly and depositing upon the central internal surface of said screenportion a quantity of viscid coating material in an amount substantiallyexceeding that required to coat said screen portion; tilting said cap ata first rate and rotating said cap at a first speed both of which arechosen in relation to the quantity and viscosity of said coatingmaterial to distribute said coating material over said screen portion assaid cap is positioned in a first tilt plane substantially less than 90degrees relative to said horizontal plane; thereafter increasing saidtilting rate to quickly position said cap in a second tilt plane of theorder of 90 degrees relative to said horizontal plane;

interrupting the tilting of said cap and removing excess coatingmaterial therefrom while said cap is in one of said tilt planes;

and drying said coating while rotating said cap in said second tiltplane at a higher speed than said first speed.

2. In the manufacture of a cathode-ray tube of the type having a capsection with a screen portion bounded by a peripheral flange, the methodof selectively coating the internal surface of said screen portion whichcomprises:

supporting said cap in a horizontal plane With said quantity of viscidcoating material in an amount sub-.

stantially exceeding that required to coat said screen portion; tiltingsaid cap at a first rate and rotating said cap at a first speed both ofwhich are chosen in relation to the quantity and viscosity of saidcoating material to distribute said coating material over said screenportion as said cap is tilted to a plane of the order of 30 degreesrelative to said horizontal plane;

interrupting the tilting of said cap While maintaining its rotation andremoving excess coating material from said cap;

resuming the tilting of said cap at a rate exceeding said first rate toquickly position said cap in a predetermined tilt plane of the order ofdegrees relative to said horizontal plane;

and drying said coating While rotating said cap in said predeterminedplane at a higher speed than said first speed.

3. In the manufacture of a cathode-ray tube of the type having a capsection with a screen portion bounded by a peripheral flange, the methodof selectively coating the internal surface of said screen portion whichcomprises:

supporting said cap in a horizontal plane with said flange extendingupwardly and depositing upon the central internal surface of said screenportion a quantity of viscid coating material in an amountsubstantially. exceeding that required to coat said screen portion;

tilting said cap at a in relation to the quantity and viscosity of saidcoating material until the charge of coating material extends to theedge of said screen portion;

interrupting the tilting of said cap for a predetermined hold interval;

removing excess coating material from said cap;

resuming the tilting of said cap at a rate exceeding.

said first rate to quickly position said cap in a predetermined tiltplane;

and drying said coating while rotating said cap in said predeterminedplane at a higher speed than said first speed.

4. In the. manufacture of a cathode-ray tube of the type having a capsection with a screen portion bounded by a peripheral flange, the methodof selectively coating the internal surface of said screen portion whichcomprises:

supporting said cap in a horizontal plane with said flange extendingupwardly and depositing upon the surface of said screen portion aquantity of viscid coating material in an amount substantially exceedingthat required to coat said screen portion;

tilting said cap at a first rate and rotating said cap at a first speedboth of which are chosen in relation to the quantity and viscosity ofsaid coating material to distribute said coating material over saidscreen portion as said cap is tilted to a plane at an angle ofapproximately 30 degrees relative to said horizontal plane;

interrupting the tilting of said cap at a tilt angle .of

approximately 30 degrees and removing and reclaimin excess coatingmaterial from said cap;

resuming the tilting of said cap at a rate exceeding said first rate toquickly position said cap at a tilt angle of the order of 90 degrees;

and rotating said cap While at said tilt angle of the order of 90degrees at a higher speed than said first speed to dry said coating. 5.In the manufacture of a cathode-ray tube of the type having a capsection with a screen portion bounded by a peripheral flange, the methodof selectively coating first constant rate and rotating said cap at afirst speed both of which are chosen 9 the internal surface of saidscreen portion which comprises:

supporting said cap in a horizontal plane with said flange extendingupwardly and depositing upon the central internal surface of said screenportion a quantity of viscid coating material at least in an amountrequired to coat said screen portion; tilting said cap at a first rateand rotating said cap at a first speed both of which are chosen inrelation to the quantity and viscosity of said coating material todistribute said coating material over said screen portion withoutcontacting any appreciable portion of said flange with said coatingmaterial as said cap is tilted from said horizontal plane by an angularamount substantially less than 90 degrees; removing any excess materialfrom said cap;

thereafter increasing said tilting rate to quickly position said cap ina predetermined tilt plane of the order of 90 degrees relative to saidhorizontal plane;

and drying said coating while rotating said cap in 5 said predeterminedplane at a higher speed than said first speed.

References Cited UNITED STATES PATENTS 10 2,821,160 1/1958 Atti 11856 X2,902,973 9/1958 Weingarten et 'al. 118-56 3,143,435 8/1964 Martyny11733.5

5 ALFRED L. LEAVITT, Primary Examiner.

H. COHEN, Assistant Examiner.

